1. Field of the Invention
The present invention relates to control of the elongation of a work to be rolled in a rolling equipment applied to a steel process line.
2. Description of the Prior Art
In a rolling equipment, generally, for a high accuracy of thickness of a steel plate as the work, the elongation of the work is controlled. An example of such a control is disclosed in "TEKKO BENRAN (IRON AND STEEL HANDBOOK) III(I)", published by the Iron and Steel Institute of Japan in 1980, on pages 674 to 676, in which tension control and rolling load control are performed respectively by feedback control systems.
A conventional device of this type is shown in FIG. 1. In the figure, numeral 1 denotes a rolling mill for skinpass rolling of the work, numeral 2 a strip as the work, numeral 3 a bridle roll located on the entrance side of the mill 1, numeral 4 a motor for driving the entrance-side bridle roll 3 to rotate, numeral 5 a pulse oscillator fitted to the entrance-side bridle roll, numeral 6 a motor for driving the work roll of the rolling mill 1 to rotate, numeral 7 a bridle roll located on the exit side of the rolling mill 1, numeral 8 a motor for driving the exit-side bridle roll 7 to rotate, and numeral 9 a pulse oscillator fitted to the exit-side bridle roll 7. Numeral 10 denotes a screw down device for exerting a load on the strip 2, numeral 11 a tensiometer for detecting the tension on the strip 2 between the entrance-side bridle roll 3 and the rolling mill 1, and numeral 12 denotes a tensiometer for detecting the tension on the strip 2 between the rolling mill 1 and the exit-side bridle roll 7. Numerals 13, 14 and 15 denote feed rate controllers for controlling the rotational speeds of the motors 4, 6 and 8, respectively, numeral 16 a tension controller by which the difference between a reference tension t.sub.1REF and the actual tension measured by the tensiometer 11 is given to the speed controller 14 as a speed signal to thereby control the tension between the entrance-side bridle roll 3 and the rolling mill 1 to be constant, numeral 17 a tension controller by which the difference between a reference tension t.sub.2REF and the actual tension measured by the tensiometer 12 is given to the speed controller 15 as a speed signal to thereby control the tension between the exit-side bridle roll 7 and the rolling mill 1 to be constant, and numeral 18 denotes a tension compensating device which receives a signal indicative of the difference between the actual tension measured by the tensiometer 11 and the reference tension t.sub.1REF and outputs a signal for correcting the tension between the exit-side bridle roll 7 and the rolling mill 1. Further, numeral 19 denotes a elongation detector for detecting the speed difference between the entrance-side bridle roll 3 and the exit-side bridle roll 7 to measure the elongation of the work, and numeral 20 denotes a elongation control unit which receives a signal indicative of the difference between the elongation detected by the elongation detector 19 and a reference elongation E.sub.ref and outputs to the screw down device 10 a rolling load regulating signal for reducing the difference signal to zero.
Operations of the device will now be explained. First, the strip 2 is fed from the entrance side to the exit side of the rolling mill 1 as indicated by an arrow, while the elongation is measured based on the signals from the pulse oscillators 5 and 9 and the rolling load is regulated so that the measured elongation accords with the reference elongation E.sub.ref. Next, when the measured elongation is varied due to some disturbance, the ratio of the number of pulses outputted by the pulse oscillator 5 in accordance with the rotational speed of the entrance-side bridle roll 3 to the number of pulses outputted by the pulse oscillator 9 in accordance with the rotational speed of the exit-side bridle roll 7 is varied, and a difference is generated between the elongation detected by the elongation detector 19 and the reference elongation. The difference signal is inputted to the elongation control unit 20, which outputs to the screw down device 10 a rolling load correction signal for reducing the elongation difference to zero, and the screw down device 10 applies a rolling load based on the correction signal to the strip 2. Besides, in order that the tension on the strip 2 between the entrance-side bridle roll 3 and the rolling mill 1 and the tension on the strip between the mill 1 and the exit-side bridle roll 7 are constantly fixed, the tension controllers 16 and 17 output speed correction signals to the speed controllers 14 and 15, thereby maintaining both of the tensions at the respective reference values.
Thus, the elongation of the work is controlled by regulating the rolling load exerted on the strip 2 by the rolling mill 1 while maintaining respectively fixed tensions on the strip 2 on the entrance side and exit side of the rolling mill 1.
In the above-mentioned conventional tension control system, however, the minor loop for correcting the rolling load and the minor loop for correcting the tension are independent of each other and, therefore, a variation in the rolling load is followed by a variation in the tension, which has a disturbing effect on the tension control system, resulting in poor response property of the elongation control.